Abstract

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Long-term oxygen therapy prolongs life in patients with COPD and severe daytime hypoxemia. Portable delivery systems, including portable oxygen concentrators (POCs), frequently incorporate delivery of short bursts, or pulses, of oxygen triggered by patient inspiration. In order to trigger a pulse of oxygen from a POC, a patient must generate a sufficiently high signal pressure to exceed the trigger threshold of the device. For standard nasal cannulas, signal pressure varies with inspiratory flow rate, cannula prong geometry, and patient nasal airway geometry. Triggering pulse delivery from POCs is frequently compromised when inspiratory flow rates are low, as occurs during sleep. The present work presents a new pillows-type nasal interface designed to improve inspiratory triggering when used with POCs. Methods: Realistic adult nasal airway replicas described previously in the study of continuous and pulsed oxygen delivery (Chen et al., 2017) were employed. Replicas previously identified as generating high (Subject 2) and low (Subjects 6 and 9) signal pressures were selected from a larger set consisting of 15 replicas. Signal pressures monitored through a single-lumen straight nasal cannula, a flared nasal cannula, and the new nasal interface were measured at inspiratory flow rates ranging from 10 to 40 L/min. The nasal interface includes adjustable channels for entrainment of room air, here referred to as settings A and B. Subsequent in vitro experiments were conducted during simulated breathing to assess oxygen delivered from a POC (SimplyGo Mini; Philips Respironics) using the new nasal interface versus straight and flared nasal cannulas. In vitro methods were consistent with those previously reported by Chen et al. (2019). Results: The new nasal interface produced higher signal pressures compared with the straight and flared cannulas. In addition, variability in signal pressure between replicas was greatly reduced when using the new nasal interface. For example, measured signal pressures for each replica at an inspiratory flow rate of 20 L/min are shown in Table 1. In vitro experiments demonstrated higher fractions of inhaled oxygen for the new nasal interface than for the straight or flared nasal cannula in circumstances where triggering was ineffective for the two nasal cannula types. Conclusion: The new nasal interface provided higher and more consistent signal pressures compared to the straight or flared nasal cannula across the airway replicas and flow rates tested. This translated into improved in vitro oxygen delivery in circumstances where triggering was ineffective for the straight and flared nasal cannula.

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